US President Donald Trump on Friday blamed Democrats for his decision to lay off thousands of workers across the US government as he followed through on his threat to cut the federal workforce during the government shutdown.

Job cuts were under way at the Treasury Department, the US health agency, the Internal Revenue Service and the departments of education, commerce, and Homeland Security's cybersecurity division, spokespeople said, but the total extent of the layoffs was not immediately clear. Roughly 300,000 federal civilian workers had already been set to leave their jobs this year due to a downsizing campaign initiated earlier this year by Trump.

"They started this thing," Trump told reporters during an event in the Oval Office, calling the job cuts "Democrat-oriented."

Trump's Republicans hold majorities in both chambers of Congress, but need Democratic votes in the US Senate to pass any measure that would fund the government.

Democrats are holding out for an extension of health-insurance subsidies, arguing health costs will increase dramatically for many of the 24 million Americans who get their coverage through the Affordable Care Act.

Trump has repeatedly threatened to fire federal workers during the shutdown standoff, in its 10th day on Friday, and has suggested his administration will aim primarily at parts of the government championed by Democrats.

Trump has also ordered the freezing of at least $28 billion in infrastructure funds for New York, California and Illinois - all home to sizable populations of Democratic voters and critics of the administration.

The Justice Department said in a court filing more than 4,200 federal employees had gotten layoff notices at seven agencies, including more than 1,400 at the Treasury Department and at least 1,100 at the Department of Health and Human Services.

Democrats say they won't relent

Democrats said they will not cave to Trump's pressure tactics.

"Until Republicans get serious, they own this - every job lost, every family hurt, every service gutted is because of their decisions," Senate Democratic Leader Chuck Schumer said.

Labor unions representing federal workers have sued to stop the layoffs, saying they would be illegal during a shutdown.

The administration said in a Friday court filing that the unions' request should be denied because they lack the legal right to sue over federal personnel decisions.

A federal judge is due to hear the case on October 15.

The government is required by law to give workers 60 days' notice ahead of any layoffs, though that can be shortened to 30 days.

Some Republicans objected to the layoffs, including Senator Susan Collins, the chair of the Senate Appropriations Committee.

"Regardless of whether federal employees have been working without pay or have been furloughed, their work is incredibly important to serving the public," Collins said in a statement.

Targeting furloughed workers

Earlier in the day, White House budget director Russell Vought wrote on social media that: "The RIFs had begun," referring to so-called reductions in force. A spokesperson for the budget office characterized the cuts as "substantial," without offering further details.

The announcement came on the same day that many federal workers were due to get reduced paychecks that do not include any pay for the days since the shutdown began. Hundreds of thousands have been ordered not to report to work, while others have been ordered to keep working without pay. The nation's 2 million active-duty troops will miss their October 15 paycheck entirely if the shutdown is not resolved before then.

Employees across multiple divisions of the Department of Health and Human Services have received layoff notices, communications director Andrew Nixon said. The 78,000 workers at the sprawling agency monitor disease outbreaks, fund medical research, and perform a wide range of other health-related duties.

Nixon said the layoffs were targeted at agency staff who have been ordered not to work, but did not provide further details. Roughly 41% of agency staff have been furloughed.

Layoffs have also begun at the Treasury Department, according to a spokesperson who requested anonymity.

A labor union official, Thomas Huddleston of the American Federation of Government Employees, said in a court filing he had been told Treasury was preparing 1,300 layoff notices. Those layoffs could hit the tax-collecting Internal Revenue Service, which has been targeted for steep job cuts this year. Some 46% of the agency's 78,000 employees were furloughed on Wednesday.

Layoffs have also begun at the Department of Housing and Urban Development, the union said.

Officials also confirmed job cuts at the Education Department, which Trump has vowed to shutter completely, and the Commerce Department, which handles weather forecasting, economic data reports, and other tasks.

Other media outlets reported layoffs at the Environmental Protection Agency, the Department of Energy and the Department of Interior. Spokespeople at those agencies did not immediately respond to requests for comment.

The Department of Homeland Security said layoffs were taking place at the Cybersecurity and Infrastructure Security Agency, which incurred Trump's wrath after the 2020 election when its director said there was no evidence voting systems were compromised. Trump falsely claims that he lost that election to Democrat Joe Biden due to voter fraud.

The Department of Transportation and the Federal Aviation Administration are not affected, according to a source familiar with the situation.